Cancel pending downgrade for a subscription contract

Important Notes:

• The downgrade must be pending (not yet executed) to be cancelled
• Once cancelled, the subscription will remain on its current plan
• An activity log entry is created when a downgrade is cancelled

Use Cases:

• Allow customers to change their mind about a scheduled downgrade
• Cancel downgrades when customers upgrade or renew
• Administrative cancellation of pending plan changes

Authentication: Requires API key authentication via X-API-Key header or api_key parameter